The present invention relates to a pattern exposure method and apparatus for projecting a circuit pattern on a circuit member by a charged particle beam passing through a pattern exposure mask, and a method and system for fabricating a semiconductor integrated circuit by utilizing the pattern exposure method and apparatus. The present invention also relates to a pattern exposure mask used for exposure of a circuit pattern of the integrated circuit, a method for forming the pattern exposure mask, and an integrated circuit having a layer/film patterned by the exposure.
Recently, an integrated circuit such as an LSI (large scale integrated circuit) is widely utilized in various fields, and therefore, an increased integration density and an elevated productivity are strongly demanded. At present, a means for forming a circuit pattern in the integrated circuit includes an optical printing and a direct drawing using an electron beam. The resolution of the optical printing is not so high as that of the electron beam drawing, but the productivity of the electron beam drawing is not so high as that of the optical printing.
In general, in the optical printing, a circuit pattern is projected by a transmission light passing through a pattern exposure mask. In the electron beam drawing, on the other hand, an electron beam is magnetically deflected and scanned to directly draw the circuit pattern. At the present, however, there is a technology for causing the electron beam to pass through the pattern exposure mask to project the circuit pattern.
However, in the optical printing using the pattern exposure mask, the circuit pattern is projected by only the transmission light. However, in the electron beam projection using the pattern exposure mask, not only the circuit pattern is projected by a transmission electron beam, but also a background exposure is caused because of a scattering beam.
In this case, since the exposure strength of the circuit pattern by the transmission electron beam is intensified by the background exposure caused by the scattering beam, the radiation strength of the electron beam can be reduced.
Now, one prior art example of the above mentioned pattern printing system will be described with reference to FIGS. 9 to 12B.
FIG. 9 is a diagrammatic view of an essential part of an electron beam projection apparatus. FIG. 10A is a diagrammatic plan view showing a structure of a pattern exposure mask, and FIG. 10B is a diagrammatic sectional view of the pattern exposure mask. FIGS. 11A, 11B, 12A and 12B illustrate the order of the pattern printing method. FIGS. 11A and 12A are diagrammatic views schematically showing the relation between the pattern exposure mask and the electron beam that is a charge particle beam. FIGS. 11B and 12B are diagrams showing the exposure strength on the circuit member.
The shown electron beam projection apparatus, generally designated with the reference number 100, has a pattern exposure mask 200 which is a replaceable parts. The pattern exposure mask 200 has a plurality of exposure regions 201. Specifically, as shown in FIG. 10A, the pattern exposure mask 200 is formed in the form of a square plate, and a number of square exposure regions 201 are arranged in the form of matrix having a number of rows and a number of columns. The square exposure regions 201 are separated from one another by a boundary region 202.
Furthermore, since the pattern exposure mask 200 is so configured to project the circuit pattern of one circuit member by one pattern exposure mask, the circuit pattern of the one circuit member is divided into a plurality of circuit sub-patterns, and the plurality of square exposure regions 201 in the one pattern exposure mask 200 correspond to the plurality of circuit sub-patterns, respectively. Therefore, each of the plurality of square exposure regions 201 in the one pattern exposure mask 200 includes a plurality of beam transmission parts 203 and a plurality of beam scattering parts 204. As shown in FIG. 11A, the beam transmission parts 203 are formed of through-holes formed in the pattern exposure mask 200 formed of silicon, and therefore, correspond to a shape of a portion to be exposed. The beam scattering parts 204 and the boundary region 202 are the remaining parts of the pattern exposure mask 200 excluding the beam transmission parts 203, and therefore, correspond to a shape of a portion that should not be exposed.
The pattern exposure mask 200 is formed of an SOI (silicon on insulator) substrate which is a multi-layer substrate, and therefore, one layer remains on the boundary region 202 as a reinforcing support 205. The pattern exposure mask 200 having the above mentioned structure is removably fitted on a predetermined place in the electron beam projection apparatus 100.
This electron beam projection apparatus 100 includes an electron gun 101 as a beam irradiator for irradiating the electron beam (as the charged particle beam) onto the pattern exposure mask 200. At an opposite side of the pattern exposure mask 200, a holder stage 102 is provided as a member holding means for holding a silicon wafer 103 which is a circuit member to be exposed.
In the way of the path passing from the electron gun 101 through the pattern exposure mask 200 to the silicon wafer 103, various electron optical systems 104 and 1054 and an aperture 106 are located so as to adjust the focusing and the reduction of an image of the electron beam projected onto the silicon wafer 103.
In the electron beam projection apparatus 100, furthermore, an irradiating and scanning means. (not shown) is constituted of a displacement mechanism (not shown) for vertically and horizontally displacing the electron gun 101, and a scanning mechanism (not shown) for vertically and horizontally deflecting the electron beam irradiated from the electron gun 101 onto the pattern exposure mask 200. By action of this irradiating and scanning means, the electron beam from the electron gun 101 is irradiated for each of the exposure regions 201 in the pattern exposure mask 200, region by region in order.
Similarly, an irradiation adjusting means (not shown) is constituted of a displacement mechanism (not shown) for vertically and horizontally displacing the holder stage 102 holding the silicon wafer 103, and a scanning mechanism (not shown) for vertically and horizontally deflecting the electron beam from passing through the pattern exposure mask 200 to be irradiated onto the silicon wafer 103. By action of this irradiation adjusting means, a corresponding number of irradiation regions of the electron beam passing through the plurality of exposure regions 201 in the pattern exposure mask 200 is located closely to one another in order on a surface of the silicon wafer 103 held on the holder stage 102, with no unexposed region corresponding to the boundary region 202 being interposed between the irradiation regions.
Thus, the electron beam projection apparatus 100 having the above mentioned features, a resist film formed on the silicon wafer 103 is exposed by the electron beam in accordance with the circuit pattern of the pattern exposure mask 200. In this case, the electron beam from the electron gun 101 is irradiated onto each of the plurality of exposure regions 210 in the pattern exposure mask 200, one by one, in the order, by action of the irradiation scan means.
Simultaneously, the irradiation regions of the electron beam having passed through the respective exposure regions 201 in the pattern exposure mask 200 are located closely to one another on the surface of the silicon wafer held on the holder stage 102, with no unexposed region corresponding to the boundary region 202, by action of the irradiation adjusting means.
Accordingly, as shown in FIGS. 11A, 11B, 12A and 12B, the exposure regions 201 are located in the pattern exposure mask 200 with the boundary region 202 being between each pair of adjacent exposure regions. On the surface of the silicon wafer 103, however, the irradiation regions of the electron beam passing through the respective exposure regions 201 in the pattern exposure mask 200 are located adjacent to one another with no unexposed region corresponding to the boundary region 202. The circuit pattern which is divided into the plurality of exposure regions 201 separated from one another by the boundary region 202 in the pattern exposure mask 200, becomes one continuous pattern again on the surface of the silicon wafer 103.
In this process, the circuit pattern is projected onto the silicon wafer 103 by the electron beam passing through the beam transmission part 203 within the exposure region 201 of the pattern exposure mask 200. Simultaneously, the background exposure occurs because of the electron beams scattered by the beam scattering part 204 and the boundary region 202. As a result, the exposure strength of the circuit pattern by the transmission beam is intensified by the background exposure attributable to the scattering beam.
Here, in the example mentioned above, a number of square exposure regions 201 are arranged vertically and horizontally in the pattern exposure mask 200 of the square plate. The beam transmission part 203 is formed of a through-hole corresponding to a shape to be exposed, and the beam scattering part 204 and the boundary region 202 are formed of the remaining part corresponding to an area which should not be exposed.
However, a pattern exposure mask 300 as shown in FIGS. 13A, 13B and 13C is known, which includes a number of elongated exposure regions 301 in the form of a stripe extending vertically. The elongated exposure regions 301 are arranged in a horizontal direction and separated from one another by an elongated boundary region 302. In this type of pattern exposure mask 300, it is a general practice that the boundary region 302 and a beam scattering part 303 are formed of a heavy metal layer laminated on a lower surface, and a beam transmission part 304 is constituted of a part from which the heavy metal layer is removed.
In this type of pattern exposure mask 300, since the beam transmission part 304 is not a through-hole, the beam transmission part 304 can be formed for example in a toroidal shape. In addition, since an overall mechanical strength is excellent, it is possible to make the exposure region 301 in the strip shape so as to elevate the productivity of the mask formation and the exposure.
In this type of pattern exposure mask 300, on the other hand, since a thin silicon plate remains in the beam transmission part 304, the electron beam passing through the beam transmission part 304 is scattered to some degree, with the result that the exposure resolution lowers. The above mentioned pattern exposure masks 200 and 300 have the advantage and the disadvantage, respectively, and therefore, an optimum one should be selected in accordance with various conditions.
As mentioned above, in the pattern exposure method using the pattern exposure apparatus mentioned above, the circuit pattern divided into the plurality of exposure regions 201 in the pattern exposure mask 200 can be projected as one continuous image on the silicon wafer 103.
However, the plurality of exposure regions 201 separated from one another by the boundary region 202 are projected in order on the surface of the silicon wafer 103 in such a manner that the projected image of the plurality of exposure regions 201 are located adjacent to one another on the surface of the silicon wafer 103. In this process, the electron beam scattered by the intervening boundary region 202 is repeatedly irradiated on the same position in a first electron beam shot for one exposure region 201 (as shown in FIGS. 11A and 11B) and a succeeding second electron beam shot for an adjacent exposure region 201 (as shown in FIGS. 12A and 12B).
In this case, as shown in FIG. 12B, the strength of the background exposure becomes excessive at the position to which the scattering beam is repeatedly irradiated. In this case, the line width of the circuit pattern projected by the transmission beam passing through the beam transmission part 203 becomes large, with the result that the circuit pattern is short-circuited in the worst case. This problem occurs not only in the pattern exposure mask 200 but also in the pattern exposure mask 300, and becomes more serious if the resolution of the circuit pattern to be exposed is elevated.
Accordingly, it is an object of the present invention to provide a pattern exposure method and apparatus for projecting a circuit pattern on a circuit member by a charged particle beam passing through a pattern exposure mask, which have overcome the above mentioned problems of the prior art.
Another object of the present invention is to provide a pattern exposure method and apparatus capable of substantially equalizing the background exposure.
Still another object of the present invention is to provide a method and system for fabricating a semiconductor integrated circuit by utilizing the pattern exposure method and apparatus.
A further object of the present invention is to provide a pattern exposure mask capable of substantially equalizing the background exposure, a method for forming the pattern exposure mask, and an integrated circuit having a layer/film patterned by the exposure substantially equalizing the background exposure.
According to a first aspect of the present invention, there is provided a pattern exposure method using a pattern exposure system which comprises a pattern exposure mask including a plurality of exposure regions which are separated from one another by a boundary region and which correspond to a plurality of circuit sub-patterns obtained by dividing one circuit pattern, each of the exposure regions including a plurality of beam transmission parts and a plurality of beam scattering parts, and a beam irradiating means for irradiating a charged particle beam to the pattern exposure mask, the method including the step of irradiating the charged particle beam from the beam irradiating means to each of the plurality of exposure regions in the pattern exposure mask in the order, so as to cause the transmitted charged particle beam passing through the beam transmission parts of the exposure region in the pattern exposure mask, to a circuit member to be exposed, so that irradiation areas of the charged particle beam passing through the respective exposure regions in the pattern exposure mask, are arranged adjacent to one another on a surface of the circuit member with no intervening portion corresponding to the boundary region, while permitting a background exposure attributable to the charged particle beam scattered by the beam scattering parts and the boundary region, wherein the charged particle beam scattered by the boundary region in the pattern exposure mask is restrained to a predetermined range.
According to a second aspect of the present invention, there is provided a pattern exposure system comprising a pattern exposure mask including a plurality of exposure regions which are separated from one another by a boundary region and which correspond to a plurality of circuit sub-patterns obtained by dividing one circuit pattern, each of the exposure regions including a plurality of beam transmission parts and a plurality of beam scattering parts, and a beam irradiating means for irradiating a charged particle beam to the pattern exposure mask, the pattern exposure system being so configured to irradiate the charged particle beam from the beam irradiating means to each of the plurality of exposure regions in the pattern exposure mask in the order, so as to cause the transmitted charged particle beam passing through the beam transmission parts of the exposure region in the pattern exposure mask, to a circuit member to be exposed, so that irradiation areas of the charged particle beam passing through the respective exposure regions in the pattern exposure mask, are arranged adjacent to one another on a surface of the circuit member with no intervening portion corresponding to the boundary region, while permitting a background exposure attributable to a charged particle beam scattered by the beam scattering parts and the boundary region, the pattern exposure system also comprising the charged particle beam restraining means for restraining the charged particle beam scattered by the boundary region in the pattern exposure mask, to a predetermined range.
According to a third aspect of the present invention, there is provided a pattern exposure mask including a plurality of exposure regions which are separated from one another by a boundary region and which correspond to a plurality of circuit sub-patterns obtained by dividing one circuit pattern, each of the exposure regions including a plurality of beam transmission parts and a plurality of beam scattering parts, the pattern exposure mask including a charged particle beam restraining means for restraining the charged particle beam scattered by the boundary region in the pattern exposure mask, to a predetermined range.
Preferably, the charged particle beam restraining means is provided on the pattern exposure mask so that when the charged particle beam is irradiated in the order to a pair of adjacent exposure regions in the pattern exposure mask, the exposure strength of a portion on the circuit member which is repeatedly exposed by the background exposure contributable to the charged particle beam scattered by the intervening boundary region between the pair of adjacent exposure regions irradiated in the order, becomes the same as the exposure strength of one background exposure contributable to the charged particle beam scattered by the beam scattering part.
In one embodiment, the charged particle beam restraining means is constituted of a film formed on at least one of an upper surface and a lower surface of the boundary region in the pattern exposure mask. For example, the film is formed of a heavy metal.
In another embodiment, the charged particle beam restraining means is constituted of a support remaining on the boundary region in the pattern exposure mask.